Haemonchus contortus resistance to monepantel in sheep: fecal egg count reduction tests and randomized controlled trials

Abstract

Worm infections are a major cause of economic losses in sheep farming, and their control depends essentially on anthelmintic drugs. After decades without the discovery of new drug types, a new class of anthelmintics, called aminoacetonitrile derivatives, represented by monepantel, was released on the market. In order to evaluate a report of low efficacy of monepantel on a sheep farm in the municipality of Taiúva, state of São Paulo, Brazil, fecal egg count reduction and critical tests were performed on a Haemonchus contortus strain collected from this farm. To this end, ten animals were experimentally infected with 5000 H. contortus third-stage larvae, and these animals were divided into two groups, control and treated, according to the treatment with monepantel. The parameters evaluated were reduction in fecal egg counts on post-treatment days (PTD) 0, 2, 4, 7 and 14, and the therapeutic efficacy at the end of this period. Egg count reduction was observed starting on PTD 2, with a maximum reduction of 32.89% recorded on PTD 14. The critical test revealed 24.65% efficacy, indicating resistance to the active ingredient monepantel. The ineffectiveness of monepantel may be associated with the excessive use of the anthelmintic, which the farmer administered at intervals of less than one month, without technical guidance or a defined criterion. Given that the anthelmintic was used on this farm for less than one year, according to the farmer, it can be inferred that H. contortus develops resistance to monepantel in a few generations if the product is used incorrectly. ResumoVerminoses são uma das principais causas de prejuízo econômico na ovinocultura, cujo controle depende essencialmente de fármacos anti-helmínticos. Depois de décadas sem o surgimento de novos grupos químicos de fármacos, uma nova classe de anti-helmínticos, os derivados da aminoacetonitrila, representados pelo monepantel, foram lançados no mercado. Com o objetivo de avaliar um relato de baixa eficácia do monepantel em uma propriedade produtora de ovinos do município de Taiúva, estado de São Paulo, foi realizado um teste de redução de contagem de ovos e um teste crítico em uma linhagem de Haemonchus contortus obtida da propriedade. Dez animais foram infectados experimentalmente com 5000 larvas de terceiro estágio do isolado de Haemonchus contortus, e estes animais foram divididos em dois grupos, controle e tratados, em dependência do tratamento com monepantel. Foram avaliados a redução de ovos nas fezes nos dias 0, 2, 4, 7 e 14 pós-tratamento e a eficácia terapêutica ao final do período. A redução da contagem de ovos foi observada a partir do 2 o dia pós-tratamento (DPT), com redução máxima, de 32,89%, registrada no 14º DPT. O teste crítico revelou eficácia de apenas 24,65%, evidenciando resistência ao princípio ativo. A ineficácia do monepantel pode estar associada a utilização do vermífugo de forma massiva, uma vez que o produtor administrava o produto em intervalos inferiores a um mês, sem orientação técnica ou critério definido. Dado que...

Losses caused by gastrointestinal nematode infections in Dorper lambs under two nutritional status

“…It is a blood-sucking parasite that causes, in acute infections, mortality, which is considered the most important economic effect attributable to this parasite (BARGER & COX, 1984). In addition, it presents high prolificacy and great capacity of developing anthelmintic resistance (ALBUQUERQUE et al, 2017;MARTINS et al, 2017;OLIVEIRA et al, 2017). Other trichostrongylid parasites produce significant reductions in weight gain, which is the case of Trichostrongylus colubriformis, considered the second most important nematode in sheep in Brazil (WILMSEN et al, 2014;ALMEIDA et al, 2018).…”

Resistance to monepantel in multiresistant gastrointestinal nematodes in sheep flocks in Rio Grande do Sul

“…Resistance to monepantel in sheep and goats was reported for the first time in New Zealand (SCOTT et al, 2013). Since then, resistance to this product has been detected in Uruguay (MEDEROS et al, 2014) and the Netherlands (VAN DEN BROM et al, 2015), and sheep helminths, particularly Haemonchus contortus, are resistant to monepantel in Brazilian breeds (CINTRA et al, 2016;ALBUQUERQUE et al, 2017;MARTINS et al, 2017).…”

“…Monepantel is the first molecule of an entirely new chemical group to appear on the market after more than 25 years (KAMINSKY et al, 2008). Despite the recent development of monepantel, cases of resistance to this drug were observed in sheep and goats in New Zealand (SCOTT et al, 2013), Uruguay (MEDEROS et al, 2014, and Brazil in the state of São Paulo (ALBUQUERQUE et al, 2017;MARTINS et al, 2017) and Paraná (CINTRA et al, 2016).…”

Nematode resistance to five anthelmintic classes in naturally infected sheep herds in Northeastern Brazil

“…Mederos et al (2014) and Van den Brom et al (2015) observed early resistance involving H. contortus in flocks of sheep from Uruguay and Holland, respectively. Likewise, Martins et al (2017) observed that sheep helminths, especially H. contortus, are already resistant to monepantel in a sheep herd located in the state of São Paulo.…”